Tubing anchor



J. 8. PAGE Jan. 1 1957 TUBING ANCHOR Filed June 8. 1953 1N VEN TOR. HN 5O J AT'TQQNEY- I a 5 w a A r a United States Patent This invention relates to a tubing anchor, and it is a general object of the invention to provide a simple, practical, improved anchor construction serviceable in a well I where it is desired to anchor one well part or object in another as, for instance a tubing within a casing.

In a typical situation a tubing anchor, tubular in form, is coupled in or carried by a string of tubing. located within a well casing, and the anchor is serviceable to engage the interior of the casing and thereby prevent or limit relative movement of the tubing at that point lengthwise of the casing- It is a general object of this invention to provide a tubing anchor operable by means of fluid handled or carriedby the anchor and tubing connected therewith and which is such as to provide a particularly firm and dependable engagement between the tubing and a casing in which the tubing is located.

Another object of this invention is to provide a tubing anchor of the general character referred to characterized by circumferentially spaced casing engaging shoes preferably related to the body of the anchor construction so that a plurality of the shoes are fixed relative to the body and are engageable with the casing while a single shoe is shiftable relative to the body and engages the casing.

Another object of this invention is to provide a tubing anchor including a simple, practical, durable and dependable fluid pressure actuating means serviceable to shift a casing engaging shoe relative to the body of the anchor.

A further object of this invention is to provide a fluid pressure actuated shoe operating means in an anchor, which means includes construction whereby the relatively operating parts required to fit for relative movement are protected against contamination and against foreign matter to the end that the structure will remain serviceable and unimpaired over a long period of time.

Another object of this invention is to provide a tubing anchor of the general character referred to characterized by various fits oil-construction and arrangement of parts which make possible economically practical construction without impairing the action or. ef ectiveness of the structure as a whole.

The various objects and features of my invention will be fully understood from the following detailed description of a typical preferred form and application of my invention, throughout which description reference 'is made to the accompanying. drawings, in which:

Fig. 1 is a side view of a tubing anchor embodying the present invention showing it coupling a string of tubing and showing parts broken away to illustrate details of construction. Fig. 2 is a plan section taken as indicated by line 22 on Fig. 1 and showing the anchor in a Well casing but not in gripping engagement therewith. Fig. 3 is a view similar to Fig. 2 showing the anchor operated or in pressure engagement with the casing. Fig. 4 is an enlarged, detailed view of a portion of the structure shown in sections in Fig. 1 of the drawings. Fig. 5 is a transverse sectional view taken as indicated by line 5-5 Patented Jan. 15, 1957 on Fig. 4. Fig. 6 is a plan section of a portion of the structure, being a view taken as indicated by line 6-6 on Fig. l, and Fig. 7 is a perspective view of theliner that is carried in theboss as'shown throughout the drawings. t

The anchor as provided by the present invention is adapted to be connected to or in a string of tubing T, and the tubing with the anchor thereon is adapted to be operated in a well casing C, or the like. In the particular case illustrated the anchor is shown connected in the tubing string, that is, between sections 10 of the tubing string, and collar-like couplings 11' are shown employed to connect the ends of the anchor to the sections 10 of the tubing. a y

The anchor as provided by the present invention includcs generally a body A tubular inform and adapted to be connected with the tubing as by means of cou plings. 11. The invention provides the anchor with a plurality of shoes adapted to engage the casing, and in a preferred construction there are shoes B fixed on or relative to the body of the anchor and engageable with the casing C, and there is a single shoe D carried by the body A and shiftable relative thereto to engage the casing C. A fluid pressure actuating means E is provided and is adapted to operate the shoe D relative to the body A, and this means preferably includes a part defining a cylinder and a piston operable in the cylinder. A fluid 7 handling means F is included in the construction and is adapted to separate fluid in the cylinder at each side of the piston from fluid in the Well, that is, from fluid in the body of the anchor and from fluid at the exterior of the anchor. The construction further includes other features, the details of which will be hereinafter mentioned.

The body A as provided by the present invention is an elongate tubular element, preferably a unitary element. The body is vertically disposed and is provided at its ends with coupling parts 13 serviceable to effect coupling of the body to tubing sections 10 as by means of the couplings 11. In the case illustrated the couplings or connections just referred to are simple or conventional threaded parts. I I p The body A as provided by the present invention is provided with longitudinally spaced flange-like projections 15', and these projections have opposed faces 16. The faces 16 are preferably fiat and'are located in planes transverse of the longitudinal axis of the body. In the preferred construction the flange-like projections 15 are adjacent the end portions 13 and are therefore spaced a substantial. distance apart, leaving the body with a middle portion 17 which is of substantial leng.h.

The middle portion 17 of the body is provided to ac- I of longitudinal channels 19 that extend longitudinally of the middle portion of the body between the flange-like projections 15 as will be observed from the drawings. In the case illustrated the channels 19 correspond in numher with the fiat sides 18 of the middle portion 17, and they are located between the flat sides and, in effect, separate them. The channels 19 provide ample space between the anchor and the casing C so that the anchor does not materially impede free flow of fluid in the casing C and past the anchor.

The invention contemplates an anchor construction including a plurality of circumferentially spaced shoes, and all of the shoes are carried by the body A so that they are held against movement lengthwise thereof, that is, they are heldbetween the flange-like projections 15. At least one of the shoes is fixed-relative to the body so that it will not move either lengthwise or radially relative thereto. In the preferred construction, as shown in the drawings, two shoes are thus fixed relative to body A and these are designated as the shoes B. In the preferred construction there is but one shoe movable radially relative to the body, and that is the shoe D. In the preferred construction the shoes are spaced circumferentially of the body so that they are located about 120 apart.

Each fixed shoe B may be a simple unitary element elongate in form and is preferably formed to haveshouldered ends 20 that engage or abut the faces 16 of the flange projections 15. In the case illustrated, each of the fixed shoes has a flat back 21 adapted to engage and seat upon one of the flat sides 18 of body A and it hasa front which is curved and which is preferably occupied by gripping teeth 22. The curvature of the front 22 of the fixed shoe is preferably such that the gripping teeth conform to and effectively grip the interior or curved inner wall 23 of the casing C when the anchor is engaged, as shown in Fig. 3. In accordance with the invention a suitable fastening means is provided to secure each fixed shoe to bodyA, and it is preferred, in practice, to employ a releasable fastening means for this purpose. In the drawings screw fasteners 25 are shown at the ends of each fixed shoe securing the shoe solidly on the body A.-

The movable shoe D is an elongate element prefer ably a unitary element, and it is provided with flat faces or ends 30 adaptedto slidably engage the opposed faces 16 of the flange projections 15. The shoe D 'has a fiat back 31 whichopposes one of the flat sides 18 of the body, and it has a front that is curved and which is provided with gripping teeth 33 as clearly shown in the drawings. The front of the shoe D is formed so that when the anchor is operated or engaged as shown in Fig. 3, the movable shoe seats against and has firm gripping engagement with the cylindrical wall 23 of casing C.

The operating means E, as provided by the present invention, is related to the movable shoe D and is adapted to shift that shoe radially relative to body A. The means E is primarily a fluid pressure actuating means and is preferably of the cylinder and piston type. In accordance with the invention the means E is located'to occur or act between body A and the shoe D, and in the construction illustrated, one element of the means E is a round cylinder element located on or carried by the body A at the side thereof where the shoe D is located while the other element is a piston operating in the cylinder and connected to or with the shoe D.

In the preferred construction the cylinder element of means E includes a boss 40 on the body A at the side 18 thereof opposing shoe D and located between the flangelike projections 15. The boss 40 is preferably formed integrally with the body and is provided with an opening that enters it from its outer or projecting'end that opposes the shoe, which opening carries an insert or liner 41. In the preferred construction, the boss is round in configuration and the opening in the boss is in the nature of a bore entering the boss from its outer or terminal end 42, and a portion 43 of the opening in the boss is threaded while the innermost portion 45 thereof is smooth walled or cylindrical and adjoins the flat bottom 46 of the boss opening. The insert or liner 41 is threaded into the threaded portion 43 and has a smooth turned inner end portion 45' that slidably fits into the portion 45 of the opening in the boss. Through this construction the insert or liner 41 is effectively releasably secured in the boss and is, in effect, a part thereof. The insert or liner is provided with a cylindrical inner wall 50. In accordance with the invention a suitable sealing means is provided between the boss and the insert 41,'and in the case illustrated, this sealing means includes an O-type sealing ring 51.

The piston 53 of the means E is slidably engaged in the cylindrical insert 41, and a suitable sealing means is provided between the periphery of the piston and the cylindrical wall 50 in the insert. In the case illustrated,

an O-type sealing ring 55 seals between the piston and the cylinder wall. In accordance with the invention an opening or fluid passage 56 is provided through the bottom 46 of the boss opening in the body A to establish a fluid connection between the interior of body A and the cylinder of the means B so that the pressure of fluid in the body A is communicated to the interior of the cylinder where it acts on the inner side of the piston 53.

A suitable means connects the piston 53 and the shoe D, and in the case illustrated, this means includes an extension 60 on the piston 53 projecting outward therefrom, and the outer or terminal end ofthe extension 60 is connected to or carries the shoe D. -In the particular case illustrated, a lug 61 is provided on the shoe D and projects into a socket 62 at the outer or terminal end of the extension 60 while a coupling pin 63, carried by the end portion of the extension, retains the lug in the socket.

In the preferred construction the shoe D is a substantially thick element, that is, his formed so that it has considerable depth radially of the structure. The shoe D is provided at its back, or in the portion opposing the side 18 of body A, with a recess that accommodates the boss 40 of means E. In the case illustrated the recess in the back of shoe D is formed so that it has curved Wall portions 65 which slidably receive the round or turned exterior 66 of the boss, and the recess terminates at a flat bottom 67 from which the lug 61 projects. In the case illustrated the boss is round and is substantially larger in diameter than the width of the shoe D and, consequently, the boss projects laterally of or beyond the sides 68 of the shoe D as will be apparent from a consideration of Figs. 2 and 5 of the draw- 1 ings Where the projecting corner portions 69 of the boss are shown beveled or dressed away to provide for ample clearance of the anchor in the casing C.

From the foregoing description it will be apparent that the boss 40 is a part of the body A, that is, it is rigid therewith and may be advantageously formed integral therewith to be a part thereof. The shoe D related to the body has the ends 30 abutting the opposed faces 16 of flanges 15, and it has the curved wall portions 65, formed by a recess in the shoe, engaging the exterior of the boss 40. In accordance with the invention, the parts at one of these points where there is shouldered engagement are flat while those at the other point of shouldered engagement are curved and concentric. Through this construction the shoe is, in effect, secured or anchored in or relative to the body against movement lengthwise of the body and against movement laterally of the direction that it is movable radially outward to engage the casing. In the preferred construction that has been illustrated, the shouldered engagement between the ends of the shoe D and the flanges 15 are flat shouldered engagements Whereas the shouldered engagements that occur where the shoe engages the exterior of the boss 40 are rounded, the curved wall portions 65 of the recess in the shoe being curved concentric with and fitting the turned exterior 66 of the boss.

In a preferred carrying out of the invention, a guide and stop means is provided in connection with the relatively moving elements of means E. In the construction illustrated, a stop flange 70 is provided on the insert or liner 41 at the outer end thereof and projects radially inward and has a bore 71 slidably carrying and guiding the extension 60. Ports 72 through the stop flange 70 provide open fluid connection between the exterior of the anchor and the interior of the cylinder of the means E at the outer side of the piston 53. The ports 72 act as vent openings so that fluid pressure in the cylinder of the means E is communicated to the exterior of the anchor.

The fluid handling means F is adapted to handle fluid at the means B so that fiuid from the interior of the body A as well as fluid from the exterior of the anchor is prevented from contacting the fitted working parts of 5 the means E that must be maintained. eleant-andin. good serviceable. condition it the. structure 1 is: to: operate. prop.- erly. In the construction illustrated, the parts protected. by: the meansF from thefluids in the casing .CI and. the tubing T are the insert 41 and the piston. SS' thatengagesand operates in the cylindrical. wall 50.

Inv the construction. illustrated the means F includes. an inner fluid separator .80 and an. outer fluid. separator 81.

The inner. fluid separator 80 serves to separate fluid. that enters the cylinder through the opening 56 from the fluid that operates against inner side. of. the piston 53: where the piston. slides. in the cylinder opening 50. Inthe construction illustrated, the inner separator 80. is a simple, fiat, disc-like partition slidably. carriedon aneck 83 projecting from the bottom 46 f the opening 7 inthe boss 40. The neck 83 projects into a central bore 84 entering the inner'side of the: unit formed by the piston. 53 and the. extension. 601 The neck 83 is tubular and. forms a continuation: of' the passage 56 in the: body so that fluid from the: interior. of the body- A is free to flow into the bore 84 in the piston-and eXten.-- sion unit. The separator. disc has a central. opening 85 slidably accommodating, the neck, and the bore. has a bottom and a cylindrical wall in whichv the periphery 86 of the separator is slidably received.-.

Through the construction just described and from Figs. 4 and 5 of the drawings, it will. be apparent that the separator 80 is free. toshift or work relative to the neck 83 and-relative to the piston and extension unit. The separator 80 is eflective to establish, maintain and. separate achamber x in the bore 84' from a chamber y. between the bottom 46 of the opening inboss 40 and the inner side of piston: 53. In accordance with the invention a clean and suitable fluid, such as av lubricant,

' ispreferably filled into and fully occupies the chamber y while fluid being handled by the. tubing passes. through: the opening or passage 56 to. fill or occupy the chamber x. As the piston .and extension unit moves out fromv a retractedposition, as shownin Fig. 2, to an operating position, as shown in Fig. 3,, the. chamber x increases. somewhat in. size or capacity whereas the chamber y remains of the same capacity but varies somewhat inshape since, as piston. 53 moves out, the inner separator 80 moves in on the neck 83. The separator 80 Will,.at all times, remain in the cylindrical bore 84.

The outer separator 81 is a simple. annular plate slidable on. the extension 60 adjacent the outer side of, piston 53, and. it is slidable in the cylinder opening 50- providedin the insert 41. The outer separator 81 establishes a chamber y between thejseparator 81. and the piston and a chamber. x in the insertv outward of. the v separator 81 and open to the interior of. the casing. C through the ports'72 in the stop flange. 70. Asth'e piston moves in the cylinder opening, 50, the chamber y will,. at all times, remain ofv the same size and shape Whereas the chamber x will varyv as the separator 81 moves relative to the stop flange 70. It is to be understood. that asuitable fluid, such as a lubricant, is establi'shed in and fully occupies the chamber y.

Through the means F the workingparts of the means E, that is, the liner 41 and the piston 53- where it has sliding engagement in the cylinder opening 50' in the liner are, at all times, completely guarded or. shielded from or against fluids in or from. the. tubing T, or in or from the interior casing C. Therefore, the means E will remain effective and in perfect working, condition over a long. period of time regardless of whether or not the fluids handled by the tubing or the casing. bear grit acids. or other elements or materials that might serveto damage or impair these working. parts.

In. operating the structure of the present invention, a tubing. T. carrying. the anchor can be lowered into or through a casingC while the shoe D isina. retractedposition as shown in Figs. 1 and 2. When the anchor has l 6 been located. as desired, pressure can. be established on the fluid in the body A, and this pressure is communicated" to the piston 53 of means E causing shoe D tobe forced outward relative to the body. As the shoe D' is moved or forced outward relative to the body, it engages the interior of casing C, and the anchor, as a whole, operates to an actuated position where the fixed shoes B are seated against the interior of casing C at the same time that the shoe D is seated against the interior of the casing. By having, one movable shoe D and circumferentially spaced fixed shoes B related to the body, as clearly shown in Figs. 2 and 3' of the drawings, as the pressure is developed in the structure against the means E, there is not only a pressing or bearing of the fixed shoes against the interior of the casing C but there is a Wedging of the fixed shoes in the casing with the result that the anchor provides a very effective and desirable anchoring of the tubing in the casing. In Fig. 3 of the drawi'ngs,,the arrows indicate generally the stresses that occur as the. anchor is set. The arrow a indicates the direction in which the anchored body tends to move due to the action of meansE. The other two arrows in Fig. 3 indicate the :forces that result causing the fixed shoes to bear and wedge tight against the interior of casing C..

With the construction provided, so long as fluid pressure remains inthe body A, the means E remains eflectiveto hold the anchor set. When the fluid pressure is reduced'in the body A, the means E is, in effect, released allowing the shoe D to assume a position such as is shown in Figs. 1 and 2, thus freeing the anchor from the casing. Movement or manipulation of the stringv of tubing T will cause the shoe D to be moved in.- wardly relative to the body A until it reaches the unactuated' position shownin Fig. 2 of the drawings.

Having described only a typical preferred form and application of my inventioml do not wish to be limited or restricted to the specific details herein set forth, but

wish to reserve to myself any variations or modifications 7 that may appear to those skilled in the art and fall within the scope of the following claims.

Having described my invention, I claim:

1. A tubing anchor including, an elongate tubular body having opposed flanges spaced apart longitudinally. of the body, a shoe fixed on the body to be stationary relative thereto, a movable shoe located between the flanges and spaced from the stationary shoe circumferentially of the body and movable radially of the body, the movable shoe having a back opposing the body and having a recess therein, and means adapted to operate the movable shoe including, a boss on the body, a bore in the boss and having. a bottom with a passage therethrough opening into the tubular body, the boss projecting into the recess and having a detachable liner carried in. the bore, said liner. having a cylindrical inner Wall, and a piston. slidable in the liner and carrying the movable shoe, the liner having a stop part adapted to limit outward movementof the piston therein when there is. fluid under pressure in the tubular body to. act upon the piston through said passage.

2. A tubing anchor. including, an elongate tubular body having opposed flanges spaced apart longitudinally of. the body, a shoe fixed on the body to be stationary relative thereto, a movable shoe located between the flanges and spaced from the stationary shoe circumferentially of the body and movable radially of the body, the movable shoe having a back opposing the body and havinga recess therein, and means adapted to operate the movable shoe including, a boss on the body, a bore in. the boss and having a bottom with a passage therethrough opening into the tubular body, the boss projecting into the recess and having a detachable liner carried in the. bore, said liner having a cylindrical inner wall, and a pistonslidable in the liner and carrying the movable shoe outwardly when there is fluid under pressure in the, tubular body to act upon the piston through said passage, the ends of the movable shoe being flat and slidably engaged with the said flanges, the boss having a curved exterior and the walls of the recess being curved and engaged with the exterior of the boss. I

3. A tubing anchor including, an elongate tubular body having opposed flanges spaced apart longitudinally of the body, an elongate shoe fixed on the body to be stationary relative thereto and to extend longitudinally, thereof, an elongate movable shoe located betweenthe flanges to extend longitudinally of the body and spaced from the stationary shoe circumferentially of the body and movable radially of the body, the movable shoe into the recess and having a detachable liner carried in the bore, said liner, having a cylindrical inner wall, and a piston slidable in the liner and carrying the movable shoe outwardly when there is fluid under pressure in the tubular body to act upon the piston through said passage, the boss being of greater width than the movable shoe and projecting laterally from the opposite sides thereof. 7

.4. A tubing anchor including, an elongate tubular body having opposed flanges spaced apart longitudinally of the body, an elongate shoe fixed on the body to be'stationary,

relative thereto and to extend longitudinally thereof, an elongate movable shoe located between the flanges to extend longitudinally of the body and spaced from the stationary shoe circumferentially of the body and movable radially of the body, the movable shoe having a back opposing the body and having a recess therein, and means adapted to operate the movable shoe including, a boss on the side of the body, a bore in the boss and having a bottom with a passage therethrough opening into the tubular body, the boss projecting radially into the recess and having a detachable liner carried in the bore, said liner having a cylindrical inner wall, and a piston slidable in the liner and carrying the movable shoe outwardly when there is fluid under pressure in the tubular body to act upon the piston through said passage, the boss being of greater width than the movable shoe and projecting laterally from the opposite sides thereof, the ends of the movable shoe being flat and slidably engaged with the said flanges, the boss having a curved exterior and the walls of the recess being curved and engaged with the exterior of the boss.

5. A tubing anchor including, an elongate tubular body having opposed flanges spaced apart longitudinally of the body, a shoe fixed on the body to be stationary relative thereto, a movable shoe located between the flanges and spaced from the stationary shoe circumferentially of the body and movable radially of the body, the movable shoe having a back opposing the body and having a recess therein, means adapted to operate the movable shoe outwardly when there is fluid under pressure in, the tubular body including, a boss on the body and having a bore in communication with the interior of the body through a passage therethrough'opening into the tubular body, the boss projecting into the recess and a piston slidably engaged in the bore to be acted upon by said fluid under pressure, an extension projecting from the piston to the movable shoe, and means releasably coupling the extension and movable shoe.

6. A tubing anchor including, an elongate tubular body having opposed flanges spaced apart longitudinally of the body, a shoe fixed on the body to be stationary relative thereto, a movable shoe located between the flanges and spaced from the stationary shoe circumferentially of the body and movable radially of the body, the movable shoe having a back opposing the body and hav ng a recess therein, means adapted to operate the movable 8 shoe outwardly when there is fluid under pressure in the tubular body including, a'boss on the body and having a bore in communication with theinterior of the body through a passage therethrough opening into the tubular body, the boss projecting into the recess and a piston slidably engaged in the bore to beacted upon by said fluid under pressure, an extension projecting from the piston to the movable shoe, and means releasably coupling the extension and movable shoe including a lug projecting from the movable shoe and a pin connecting the lug and extension.

7. A fluid operated tubing anchor including, an elongate tubular body having a radially disposed boss with a cylindrical opening having a fiat bottom, a neck projecting radially from the bottom of the opening and having a central fluid passage establishing open communication between the interior of the body and the opening in said boss, a shoe on the body movable radially relative thereto, a piston in the cylindrical opening and operatively connected with the shoe, the piston having a cylindrical recess opposing the body and freely receiving the neck, a body of fluid in the opening adjacent the piston, and a disc-shaped partition slidably carried on the neck and in the cylindrical recess in the piston whereby said body of fluid therein adjacent the piston is separated from fluid in the body passed by the neck.

8. A fluid operated tubing anchor including, an elongate tubular body having a radially disposed boss with a vcylindrical opening, there being a tubular neck concentric with and projecting radially into the boss from the body and forming a fluid passage in the body connecting the interior of the body and the opening in said boss, a shoe on the body movable radially relative thereto, a piston in. the cylindrical opening and operatively connected with the shoe, the piston having a cylindrical recess opposing the body, a body of fluid in the opening adjacent the piston, a disc-shaped partition slidably carried in the cylindrical recess in the piston and having an opening therein engaged over the tubular neck whereby said body of fluid therein adjacent the piston is separated from fiuid in the body passed by said passage, and flanges on the body guiding the shoe radially of the body.

9. A fluid operated tubing anchor including, an elongate tubular body having an outwardly projecting radially disposed boss with a cylindrical opening at the outer end thereof, there being a fluid passage in the body connecting the interior of the body and the cylindrical opening, a shoe on the body movable radially relative thereto, a piston in the cylindrical opening and operatively connected with the shoe, an extension projecting outward from the piston to the shoe, a body of fluid in the opencarried in the boss and having an opening therein engaged over the extension on the piston whereby said body of fluid therein adjacent the piston is separated from fluid surrounding the anchor and entering the outer end of the cylindrical opening, and a stop at the outer end portion of the boss limiting outward movement of the partition.

10. A fluid operated tubing anchor including, an elongate tubular body having an outwardly projecting radially disposed boss with a cylindrical opening open at the outer end thereof, there being a fluid passage in the body connecting the interior of the body and the cylindrical opening, a shoe on the body movable radially relative thereto, a piston in the cylindrical opening having a cylindrical recess opposing the body, outer and inner bodies of fluid in the opening and adjacent the piston, an outer movement of the outer partition, and an inner disc-shaped partition slidably carried in the cylindrical recess in the piston whereby the inner body of fluid therein adjacent the piston is separated from fluid in the body passed by said passage.

11. A fluid operated tubing anchor including, an elongate tubular body having a radially disposed boss with a cylindrical opening therein, there being a fluid passage in the body connecting the interior of the body and the cylindrical opening, a shoe on the body movable radially relative thereto, a piston in the cylindrical opening and operatively connected with the shoe, the piston having a cylindrical recess in the portion opposing the body, a body of fluid in the cylindrical opening and in the said recess in the piston, a tubular neck projecting radially from the body and in communication with said passage and extending into the recess, and a disc-shaped partition with an opening therein and slidably carried on the neck and slidably carried in the cylindrical recess whereby said body of fluid is separated from fluid in the tubular 20 body passed by said passage.

12. A fluid operated tubing anchor including, an elongate tubular body having a radially disposed boss with a cylindrical opening therein, there being a fluid passage in the body connecting the interior of the body and the cylindrical opening, a shoe on the body movable radially relative thereto, a piston in the cylindrical opening, outer and inner bodies of fluid in the opening and adjacent the piston, an extension projecting outward from the piston to the shoe, an outer disc-shaped partition with an opening therein and slidably carried on the extension and slidably carried in the cylindrical opening to retain said outer body of fluid, a stop at the outer end portion of the boss limiting outward movement of the piston, the piston having a cylindrical recess in the portion opposing the body, a tubular neck projecting radially from the body and in communication with said passage and extending into the recess, and an inner disc-shaped partition with an opening therein and slidably carried on the neck and slidably carried in the cylindrical recess to retain said inner body of fluid.

References Cited in the file of this patent UNITED STATES PATENTS 2,658,459 Page Nov. 10, 1953 

